1. Field of the Invention
This invention relates generally to optical instruments, and particularly to a lockable, double ball clamp allowing easy adjustment in five degrees of freedom.
2. Description of the Prior Art
The use of adjustable mounting or clamping devices is a common technique in the field of experimental optics. Such mounts are used to position optical elements, such as light sources and other optical devices. Since these devices do not conform to a standard set of dimensions, each may require mounting at a different vertical distance (height) above the optical bench or other work surface. These devices have widely varying sizes and shapes, and are frequently positioned in close proximity to each other. This leads to the requirement that the mount (clamp) be capable of lateral adjustment to accommodate the case where the mount for the clamp cannot be positioned directly on the optical axis of the system. The requirements are further complicated by the fact that some devices may have to be positioned at odd angles to each other and to the optical bench.
Even a minute amount of movement can have a substantial effect on the optical system being implemented, so the adjustable clamp must be rigid enough to avoid any movement once it has been set up. The required rigidity must not be obtained at the sacrifice of adjustability. In other words, the adjustable clamp must be capable of being loosened to the point where the position of the clamp can be altered. This means that the clamping action must not have "sticking" characteristics. That is, when the clamp is loosened for repositioning, there must not be a substantially larger force required to break the clamp loose than is retained by the clamp after repositioning.
While a wide variety of adjustable clamps are available, each has shortcomings. Commonly used clamps frequently utilize split bores or sockets which accommodate posts or balls and can be tightened by reducing the diameter of the bore or socket by means of a screw extending across the split. In addition to the problems discussed above, tightening of the clamp introduces movement of the optical device being positioned such that the clamp must be iteratively repositioned and tightened in a fashion to accommodate the movement induced by the tightening. In other words, the optical device must be offset from the desired position in order to accommodate the movement induced by the tightening action. This particular problem is exacerbated when the clamp tends to bind when loosened for repositioning. This leads to lengthy set up times and unduly complicates the erection of the optical system. Alternatively, this shortcoming can sometimes be overcome by the use of clamps having limited freedom of movement, but this leads to other complications and expense, for example, a requirement for more clamps. While the use of two clamps where one might suffice seems to be a small disadvantage, movement of one clamp may require that the related dependent clamp be repositioned. It may therefore be said that every additional clamp introduces complexity to the system and increases the time required for set up.
Thus, there is a need for a mechanical clamp which allows the optical device being held to be freely rotated, moved in the vertical and horizontal planes, as well as allowing displacement from the mounting point on the optical bench. All of this must be accomplished without movement introduced by tightening the clamp, or causing the clamp to stick when it is loosened for adjustment.